Digital entroping for digital audio reproductions

ABSTRACT

The present invention provides a system and method for introducing white noises into a digital audio signal so that there is progressive and cumulative degradation in audio quality after each successive reproduction of the audio sound signal in a fashion analogous to analog audio reproduction. The invention provides a white noise generator, and a digital entroping unit. In a preferred embodiment, the white noise generator is implemented by a hardware random number generator. The digital entroping unit controls the magnitude of white noise desired based on a random number generated by the random number generator, and adds the white noise to the input audio sound signal to produce a degraded audio sound signal. The magnitude of white noise can be controlled by using various masking and formatting of random number data.

FIELD OF THE INVENTION

[0001] This invention relates generally to a digital data manipulation.More specifically, the invention relates to a technique for progressivedegradation of a digital audio signal in reproduction.

BACKGROUND OF THE INVENTION

[0002] The combination of computer technology and digital audiorecording technology has made it possible to reproduce or create copiesof audio recordings with the same or almost the same quality as theoriginal recordings on media such as CD (compact disc) or DAT (digitalaudio tape). The ability to recreate digital audio recordings, forexample, music, without losing its original quality, can be a threat tocopyright owners of the music and can seriously affect revenuegeneration for the music industry.

[0003] Thus, the Audio Home Recording Act (AHRA) of 1992 (Title 17,Chapter 10, of the United States Code) was enacted to preventunrestrained and uncontrolled reproduction of music recordings publishedby the music industry. The AHRA includes provisions to place certainbuilt-in limitations in digital music that are designed to preventunauthorized reproduction of music recordings. For example, in order toavoid violation of the AHRA, an audio device must comply with the serialcopy management system (SCMS), which requires the configuration thatuses a single protection bit. Under the SCMS, the single bit protectionis reset in the original master copy, and is set in all other second orhigher generation copy versions in order to prevent unauthorizedreproductions off the second or higher generation copy versions.

[0004] The existing techniques that implement the SCMS often createsineffective and inefficient solutions to prevent unauthorizedrecordings. In particular, it is overly simple and inflexible due to thesingle bit protection scheme. The use of a single bit protection is alsooften vulnerable to attempts to circumvent it, and is often decipheredrelatively easily because modern computers are powerful andwell-equipped to break the code and decipher single bit protectionschemes. Once a single bit protection scheme is known, it is relativelyeasy to neutralize the whole protection scheme and make reproductions ofthe original music recordings at will.

[0005] Although there are more sophisticated encryption schemes toprevent unauthorized reproduction such as cryptographic watermarking andprivate copy protection scheme, they are also vulnerable tocircumvention and may be deciphered by using personal computers whoseprocessing power continues to escalate with time. In addition,cryptographic encryption schemes can be prohibitively expensive if theencryption is strong enough to prevent all unauthorized decryptionattempts.

[0006] The AHRA exempts analog recordings because analog recordings willinherently degrade each successive reproductions or copying. However,the analog exemption does not apply to popular audio recording media,such as CD, because they use a digital format for recordings, not theanalog format.

[0007] In view of the foregoing, it is highly desirable to provide aflexible, cost-efficient copy protection mechanism in compliance withthe Audio Home Recording Act. It is also desirable to provide amechanism that would be applicable to popular digital recording media,such as CD and DAT, that would prevent unauthorized reproduction whilebeing strong enough to prevent circumvention or deciphering.

SUMMARY OF THE INVENTION

[0008] The present invention provides a system and method forintroducing white noise into a digital audio data stream so that thereis progressive quality degradation after each reproduction of the audiosignals in a fashion analogous to analog audio reproduction. Theinvention may include a white noise generator, a microprocessor, and adigital entroping unit coupled to the white noise generator. In oneaspect of the invention, the digital entroping unit is embedded in themicroprocessor as part of its firmware program.

[0009] In a preferred embodiment, the invention uses a hardware basedrandom number generator as the white noise generator. Typically, anincoming audio signal comprises a plurality of digital data sampled atdifferent time points, and the random number generator generates arandom random number comprising sixteen (16) bits for each audio datasample. A masking or scaling data is applied to each random numbergenerated in order to select a predetermined number of bits from therandom number. The predetermined number of bits (the strength of thewhite noise) is then added to the original audio date to create degradedaudio data. The predetermined number of bits is determined based on thelevel of desired degradation of the audio data. In particular, variousdesired degradation levels (of hisses and pops) can be achieved by usingdifferent predetermined algorithms for modifying the masking or scalingdata. Because of the randomness of the white noise being added, it isnearly impossible to recover the original audio signal from the degradedaudio output.

[0010] In one aspect of the invention, the predetermined number of bitsof the random number is selected so that there is approximately 3 dBdegradation of the input digital audio signal as a result of digitalentroping. At 3 dB output noise, there are noticeable differences ordegradations from the original audio signal. Repeated reproductions orcopying of the audio data with 3 dB degradation will result incumulative degradation in the quality of the audio data as the digitalentroping process repeatedly injects additional white noise into thenext generation copies. Eventually, the audio data will be degraded tosuch an extent that after multiple generation of reproductions, itbecomes unrecognizable or unenjoyable to the listener. Thus, an audioquality degradation similar to analog reproduction can be achieved fordigital audio data.

[0011] In another aspect of the invention, the randomness of the digitalentroping process is in timing of adding a noise number to the inputaudio data. The invention determines whether a noise number is to beadded to the input audio data or not. The noise number is then added tocertain audio data randomly selected based upon an algorithm usingrandom numbers.

[0012] In accordance with the invention, multiple attempts to reproduceor copy the multi-generation audio signal will result in furtherdegradation in the quality of the audio signal as the digital entropingprocess is applied multiple times, thereby increasing the randomness orentropy of the audio data. After multiple reproductions the audio datawill be so degraded that it becomes unrecognizable or unacceptable tothe listener. An audio quality degradation similar to analogreproduction can thus be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a better understanding of the invention, reference should bemade to the following detailed description taken in conjunction with theaccompanying drawings, in which:

[0014]FIG. 1. is a block diagram illustrating a digital entroping systemin accordance with one embodiment of the invention;

[0015]FIG. 2(A) illustrates an analog audio signal being sampled attimes t1-t9;

[0016]FIG. 2(B) illustrates pulse code modulated audio signal withsamples D1-D9;

[0017]FIG. 3 is a flowchart illustrating a method for digital entropingfor digital audio data in accordance with one embodiment of theinvention;

[0018]FIG. 4(A) illustrates the addition of a random number to digitalaudio data according to one embodiment of the invention in which a one(1) bit LSB white noise is added to the digital audio data D3 of FIG.2(B);

[0019]FIG. 4(B) illustrates the addition of a random number to digitalaudio data according to one embodiment of the invention in which a one(1) bit LSB white noise is added to the digital audio data D4 of FIG.2(B); and

[0020]FIG. 5 is a flowchart illustrating a method for digital entropingfor digital audio data in an alternate embodiment of the invention.

[0021] Like reference numerals refer to corresponding parts throughoutthe drawings.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0022] The invention is particularly applicable to on-line and it is inthis context that the invention will be described. It will beappreciated, however, that the digital entroping unit in accordance withthe invention has greater utility, such as to other types of digitalaudio applications. To understand the digital entroping in accordancewith the invention, the basic process of the digital entroping and itsoperations will be described.

[0023] Overview—Digital Entroping

[0024] The invention introduces white noise into a digital audio signalin order to degrade the audio signal. White noise is a random noisewhose noise spectral level (noise-power density) is uniform over a widefrequency range. Once the white noise is added to the input audiosignal, it is nearly impossible to reverse the process and recover theoriginal input audio signal because of the randomness of the whitenoise. The degree of degradation can be varied by changing the amount ofthe white noise that is added to the input audio signal. Because theideal white noise, which requires an average power of infinity, does notexist in real life, the invention approximates the ideal white noise byusing a random number (RND) generator. In a preferred embodiment, theinvention may use a hardware based random number (RND) generator. Forexample, the random number generator may be constructed using linearfeedback shift registers (LFSRs) on a PLL/VCO (phase locked loop/voltagecontrolled oscillator) based clock generator. In a preferred embodiment,the initial condition of the LFSRs are randomly determined by the analogelectro-mechanical-conditions of the PLL/VCO circuits that aredetermined by the manufacturing and environmental parameters. A digitalentroping system of the invention will now be described.

[0025] Digital Entroping System

[0026]FIG. 1. is a block diagram illustrating a digital entroping system100 in accordance with one embodiment of the invention. In FIG. 1, thedigital entroping system comprises a random number generator 101, amicroprocessor 103, and a digital entroping unit 105. In a preferredembodiment, the digital entroping unit 105 is embedded in themicroprocessor 103 as part of its firmware program. In an alternateembodiment of the invention, the digital entroping unit 105 may beimplemented using hardware such as an application specific integratedcircuit (ASIC) or digital signal processor (DSP) instead of software,and may be external to the microprocessor 103. Also, in a preferredembodiment, the random number generator 101 is external to themicroprocessor 103. However, it will be apparent to one skilled in theart that the random number generator can be implemented on chip as partof the microprocessor 103 or as a piece of software executable by themicroprocessor 103.

[0027] In a preferred embodiment, the random number generator 101 isimplemented as described in greater detail in co-pending U.S. patentapplication No. 09/847,982 entitled, “Random Number Generation Methodand System,” filed May 2, 2001, which is incorporated herein byreference. It will be appreciated by one skilled in the art that othersuitable methods may be used to implement the random number generator101. In yet another embodiment of the invention, software routinesincluded in the firmware of the microprocessor 103 may be used as therandom number generator 101. Also it will be apparent to one skilled inthe art that any suitable psuedorandom number generator may be used inconjunction with the invention instead of a random number generator.

[0028] In one embodiment of the invention, the random number generator101 generates sixteen (16) bit random numbers. However, it will beapparent to one skilled in the art that other sizes and structures maybe used for the random number generator 101 so long as the generatedrandom numbers do not exhibit periodicities, or a predictable algorithm.

[0029] In operation, an incoming audio signal 107 is received by themicroprocessor 103. The microprocessor generates a random number andprovides the random number and the input audio signal to the digitalentroping unit 105 for digital entroping. After processing by thedigital entroping unit 105, the microprocessor 103 produces a degradedaudio output 109.

[0030] In more detail, the incoming digital audio signal 107 istypically a modulated signal. Especially for music sounds, the originalaudio signal is analog in nature, and it must be converted into adigital signal using well-known modulation techniques for digitalprocessing. FIG. 2(A) illustrates an analog audio signal 201 beingsampled at times t1-t9. Since the original audio signal 201 is analogand analog signals are continuous, the digitization process includessampling of the analog audio signal at some time intervals as iswell-known in the art. The sampled points are then converted intodigital data by a modulation technique. In a preferred embodiment, theaudio signal is pulse code modulated (well-known in the art andtherefore not described in detail). The analog to digital conversion maybe carried out by an analog-to-digital converter (ADC) circuit or bysoftware executable by a microprocessor.

[0031]FIG. 2(B) illustrates pulse code modulated audio data D1-D9. Inparticular, at times t1-t9, the analog audio signal is converted todigital data D1-D9, respectively. D1-D9 each comprises a plurality ofdigital bits, depending on the quantization level as is well-known inthe art. In a preferred embodiment, D1-D9 each comprise sixteen (16)bits. However, D1-D9 may have other number of digital bits as necessarywithout departing from the scope of the invention.

[0032] The pulse code modulated (PCM) audio signal may be furtherencoded for compression using a codec. Codecs are devices used to encodeand decode (or compress and decompress) various types ofdata—particularly those that would otherwise use up inordinate amountsof storage, such as audio (sound) and video files. Although a PCMtechnique is described in connection with a preferred embodiment, itwill be appreciated by one skilled in the art that other modulationtechniques can be used to digitize the analog sound signal. For exampledelta modulation (DM) can also be used to convert the analog soundsignal into digital signal. A digital entroping process for input audiosignal 107 will now be described in more detail.

[0033] Digital Entropying Process

[0034]FIG. 3 is a flowchart illustrating a method for digital entropingfor digital audio input signal 107 in accordance with a embodiment ofthe invention. The digital audio input signal 107 comprises a pluralityof digital data sampled at different time points as discussed above withreference to FIGS. 2(A) and 2(B). Each sampled digital data may comprisea plurality of digital bits.

[0035] Referring to FIG. 3, in step 301, a random number is generated bya random number generator discussed above. A new random number isgenerated for each new digital data such as D1-D9. In step 303, thegenerated random number is adjusted to the desired level of white noiseby the digital entroping unit 105. In one embodiment of the invention,this is accomplished by applying a masking or scaling data to eachrandom number generated in order to select a predetermined number ofbits from the random number and by adding the predetermined number ofbits to the audio data, or subtracting the predetermined number of bitsfrom the audio data. The predetermined number of bits is determinedbased on the level of desired degradation of the audio data. Thepredetermined number may be a signed or unsigned integer or a fixednumber. In particular, various desired degradation levels can beachieved by using different predetermined numbers and modifying themasking data. Table 1 below illustrates various masking/scaling data andcorresponding levels of white noise. TABLE 1 White Noise Masking DataOperation 1 bit LSB noise 0000000000000001 (Random number) && (0x001) 2bit LSB noise 0000000000000011 (Random number) && (0x002) 1 bit MSBnoise 1000000000000000 (Random number) >> 15 & (0x001) 2 bit MSB noise1100000000000000 (Random number) >> 14 & (0x002)

[0036] where >> operator denotes a double right shift bit operation, &denotes a bitwise AND operation, and && denotes a logical AND operation.

[0037] Referring to Table 1, in one embodiment of the invention, one (1)bit LSB (least significant bit) white noise is added to the digitalaudio input 107 by applying the mask data 0000000000000001 to each dataof the digital audio signal such as D1-D9. Alternatively, two (2) bitLSB white noise may be added by using the mask data 0000000000000011.Similarly, one (1) bit and two (2) bit MSB (most significant bit) whitenoises can be added by using 1000000000000000 and 1100000000000000,respectively. Although data in Table 1 uses sixteen (16) bit maskingdata, it will be apparent to one skilled in the art that the size of themaking data can be varied without departing from the scope of theinvention. Thus, the level of white noise can be controlled usingmasking data as illustrated in Table 1. It will be appreciated by oneskilled in the art that other levels and polarity of white noise can beachieved by using other suitable masking data and formats than thoseillustrated in Table 1.

[0038] Typically, the target degradation level is approximately 3 dB(decibel) and the appropriate masking data is selected to achieve the 3dB degradation. The dB or decibel is a ratio of output power to inputpower expressed in logarithmic terms. At 3 dB, human ears can detectnoticeable distortions or degradations from the original audio signal.Other levels of degradation may also be achieved by using differentlevels of white noise. For example, if the compliance with the AHRArequires a higher level of degradation than 3 dB, then three (3) bit orgreater LSB white noise can be used as masking data in order tointroduce a higher level of degradation into the input digital audiodata.

[0039] In a preferred embodiment of the invention, step 303 is executedby the digital entroping unit 105. For this purpose, the digitalentroping unit 105 may comprise means for selecting a predeterminednumber of bits of a random number generated and means for adding thepredetermined number of bits of the random number to digital audio dataD1-D7. Means for selecting a predetermined bits of a random number mayfurther comprise means for formatting and applying masking/scaling datato the random number. In a preferred embodiment of the invention, meansfor selecting a predetermined number of bits of a random number andmeans for adding the predetermined number of bits are implemented bysoftware. However, it will be apparent to one skilled in the art thatmeans for selecting a predetermined number of bits of a random numberand means for adding the predetermined number of bits may be implementedby hardware. For example, means for adding a predetermined number ofbits of a random number may be implemented by an adder circuit. Also,means for applying masking data to the random number may be implementedusing hardware circuitry such as a shift register and a multiplier inaccordance with an alternate embodiment of the invention.

[0040] Referring back to FIG. 3, in step 305, digital audio data such asD1 is obtained by the digital entroping unit 105. The sequence ofexecuting steps 303 and 305 may be varied without departing from thescope of the invention. For example, steps 303 and 305 may be executedsimultaneously or in any order. In step 307, the adjusted random numberis added to the input audio data. In a preferred embodiment of theinvention, the steps 305 and 307 are performed for input audio data at acertain interval of time, or may be applied to each sampled digital datasuch as D1-D9.

[0041] In step 309, the result of the addition in step 307 is producedas output audio data. In step 311, it is determined whether all inputaudio data have been processed. If so, the digital entroping processcompletes. Otherwise, the process returns to step 301 to continue thedigital entroping process. The digital entroping process completes whenall digital data such as D1-D9 are processed. The output signal 109comprises a plurality of digital data processed by the digital entropingprocess. At completion of the process, the randomness or the entropy ofthe output audio signal 109 increases and the quality of the outputaudio signal 109 decreases accordingly from its original qualitydepending on the level of the white noise introduced.

[0042]FIG. 4(A) illustrates the step 307 of FIG. 3 in greater detailaccording to one embodiment of the invention in which a one (1) bit LSBwhite noise is added to the digital audio data D3 of FIG. 2(B). The LSBof the random number being added is one (1) so that the input audiosignal D3 is altered and degraded after the addition of the one bit LSBwhite noise as shown in FIG. 4(A). FIG. 4(B) illustrates the step 307 ofFIG. 3 in greater detail according to one embodiment of the invention inwhich a one (1) bit LSB white noise is added to the digital audio dataD4. Since the LSB of the random number generated is logic low (0) inthis case, the addition of the one bit LSB white noise to D4 does notalter the input audio signal D4 as shown in FIG. 4(B).

[0043]FIG. 5 is a flowchart illustrating a method for digital entropingfor digital audio input signal 107 in an alternate embodiment of theinvention. In step 501, a noise number is generated by any suitablenumber generator such as an adder. The noise number generated in step501 may be a known number or a random number. In step 503, the numbermay be optionally adjusted to the desired level of noise by the digitalentroping unit 105. As in step 303, this may be accomplished by applyinga masking or scaling data to the number in order to select apredetermined number of bits from the number and by adding thepredetermined number of bits to the audio data, or subtracting thepredetermined number of bits from the audio data. The predeterminednumber of bits is determined based on the level of desired degradationof the audio data. The predetermined number may be a signed or unsignedinteger or a fixed number.

[0044] In step 505, it is determined whether the adjusted noise numberis to be added to the input audio data or not. In one embodiment of theinvention, this decision may be made based on a random number. In oneembodiment of the invention, a separate random number may be generatedfor this purpose. For example, an LSB or MSB of a random number may beused to make the determination of whether to add the adjusted number tothe audio data. Alternatively, more complex algorithms for processingthe random number may be used to make the determination as to whichaudio data should be added the noise number. In comparison to FIG. 3,the randomness of the digital entroping process of FIG. 5 is in timingof adding the noise number to the input audio data.

[0045] If it is determined in step 505 that the adjusted noise number isto be added to the input audio data, digital audio data such as D1 isobtained by the digital entroping unit 105 in step 507. Otherwise, theprocess continues to step 506. The sequence of executing steps 505 and507 may be varied without departing from the scope of the invention. Forexample, the steps 505 and 507 may be executed simultaneously or in anyorder. If step 507 precedes step 505 in an alternate embodiment of theinvention, step 509 may follow step 505.

[0046] In step 509, the adjusted noise number is added to the inputaudio data. In step 511, the result of the addition in step 509 isproduced as output audio data. In step 513, it is determined whether allinput audio data have been processed. If so, the digital entropingprocess completes. Otherwise, the process returns to step 506 tocontinue the digital entroping process. At completion of the process,the randomness or the entropy of the output audio signal 109 increasesand the quality of the output audio signal 109 decreases accordinglyfrom its original quality depending on the level of the white noiseintroduced.

[0047] When the routine in FIG. 3 or FIG. 5 is applied to the inputaudio signal 107 comprising digital audio data such as D1-D9, there maybe or may not be a degradation on particular digital data D1-D9depending on the random number generated for the particular input audiodata or depending on the timing of adding a noise to the digital data.For example, D1, D3, D8, and D9 may be degraded while D2, D4-D7 mayremain unaffected. But when observed as a whole, the digital entropingdegrades the input audio signal D1-D9 to the extent that depends on theparticular level of white noise being introduced. The level ofdegradation can be adjusted by applying different magnitude of whitenoise or masking/scaling data as illustrated in Table 1.

[0048] In principle, a degradation of an input audio data depends on theparticular random number generated for the input audio data, and whetherthere will be a degradation or not is a random function. Because of thisrandomness, it is nearly impossible to determine which input data of theincoming audio signal 107 is degraded and which is not, and an effort torecover the original incoming audio signal 107 based on the degradedaudio output 109 will thus fail. Even if a potential hacker is able toduplicate the exact architecture of the particular random numbergenerator being used, it is still nearly impossible to recover theoriginal incoming audio signal 107 from the degraded audio output 109because the same random number generator produces a different numbersequence each time it is activated and its outputs cannot be duplicatedor predicted accurately unless the successive of the random numbergenerator are also known.

[0049] In accordance with the invention, multiple attempts to reproduceor copy the multi-generation audio signal will result in furtherdegradation in the quality of the audio signal as the digital entropingprocess in FIG. 3 or FIG. 5 is subsequently applied multiple times,thereby increasing the randomness or entropy of the audio data.Eventually the audio data will be so degraded after multiplereproductions that it becomes unrecognizable or unacceptable to thelistener. For example, if there is a 3 dB degradation every time audiomusic data is reproduced, there will be approximately 9 dB degradationafter three (3) reproduction attempts. At 9 dB, there is a significantquality degradation so that the quality of the audio music data is nolonger enjoyable and the users are discouraged from further reproductionattempts. Thus, an audio quality degradation similar to analogreproduction can be achieved by properly adjusting the magnitude ofwhite noise or noise number being added to the audio data.

[0050] The foregoing description, for the purposes of explanation, usedspecific nomenclature to provide a thorough understanding of theinvention. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice theinvention. In other instances, well known circuits and devices are shownin block diagram form in order to avoid unnecessary distraction from theunderlying invention. The foregoing descriptions of preferredembodiments of the present invention are presented for purposes ofillustration and description. They are not intended to be exhaustive orto limit the invention to the precise forms disclosed. It will beappreciated by those skilled in he art that changes in this embodimentmay be made without departing from the principles and spirit of theinvention, the scope of which is defined by the appended claims.

1. A method for analog-like progressive degradation of a digital audiosignal to prevent unauthorized reproduction of said digital audio signalcomprising generating white noise; and degrading said digital audiosignal using said white noise to produce a degraded digital audiosignal, so that a degradation effect similar to an analog audioreproduction can be obtained.
 2. The method of claim 1 wherein saidwhite noise is a random number comprising a plurality of digital bits.3. The method of claim 2 wherein said degrading comprises adding apredetermined number of said plurality of digital bits to said digitalaudio signal.
 4. The method of claim 3 wherein said predetermined numberis one (1).
 5. The method of claim 4 wherein said adding saidpredetermined number of said plurality of digital bits comprises addinga least significant bit of said random number.
 6. The method of claim 4wherein said adding said predetermined number of said plurality ofdigital bits comprises adding a most significant bit of said randomnumber.
 7. The method of claim 3 wherein said predetermined number istwo (2).
 8. The method of claim 7 wherein said adding said predeterminednumber of said plurality of digital bits comprises adding two (2) leastsignificant bits of said random number.
 9. The method of claim 7 whereinsaid adding said predetermined number of said plurality of digital bitscomprises adding two (2) most significant bits of said random number.10. A computer program product for use in conjunction with a computersystem, the computer program product comprising a computer readablestorage medium and a computer program mechanism embedded therein, thecomputer program mechanism comprising: instructions for generating whitenoise, and instructions for degrading a digital audio signal using saidwhite noise to produce a degraded digital audio signal so that adegradation effect similar to an analog audio reproduction can beobtained.
 11. The computer program product of claim 10 wherein saidwhite noise is a random number comprising a plurality of digital bits.12. The computer program product of claim 11 wherein said degradingcomprises adding a predetermined number of said plurality of digitalbits to said digital audio signal.
 13. The computer program product ofclaim 12 wherein said predetermined number is one (1).
 14. The computerprogram product of claim 13 wherein said adding said predeterminednumber of said plurality of digital bits comprises adding a leastsignificant bit of said random number.
 15. The computer program productof claim 12 wherein said predetermined number is two (2).
 16. Thecomputer program product of claim 15 wherein said adding saidpredetermined number of said plurality of digital bits comprises addinga least significant bit of said random number.
 17. A method forprogressive degradation of a digital audio signal, comprising:generating a random number; selecting a predetermined number of bits ofsaid random number; adding said predetermined number of bits to saiddigital audio signal to produce a degraded digital audio signal, andwherein said predetermined number of bits of said random number isselected so that said degraded digital audio signal representsapproximately 3 dB difference from said digital audio signal.
 18. Themethod of claim 17 wherein said predetermined number of bits comprises aleast significant bit of said random number.
 19. The method of claim 17wherein said predetermined number of bits comprises a most significantbit of said random number.
 20. A computer program product for use inconjunction with a computer system, the computer program productcomprising a computer readable storage medium and a computer programmechanism embedded therein, the computer program mechanism comprising:instructions for obtaining a random number; instructions for selecting apredetermined number of bits of said random number; and instructions foradding said predetermined number of bits to said digital audio signal toproduce a degraded digital audio signal, wherein said predeterminednumber is selected so that said degraded digital audio signal representsapproximately 3 dB difference from said digital audio signal.
 21. Thecomputer program product of claim 20 wherein said predetermined numberof bits comprises a least significant bit of said random number.
 22. Thecomputer program product of claim 20 wherein said predetermined numberof bits comprises a most significant bit of said random number.
 23. Amethod for progressive degradation of digital audio signal comprising aplurality of pulse code modulated audio data, wherein said pulse codemodulated audio data each comprises a plurality of bits, said methodcomprising: (a) generating a random number comprising sixteen (16) bits,(b) selecting a predetermined number of bits of said random number; (c)adding said predetermined number of bits to a first pulse code modulatedaudio data of said digital audio signal; and (d) repeating (a)-(c) untilsaid plurality of pulse code modulated audio data are processed toproduce degraded digital audio signal, whereby said degraded digitalaudio signal is degraded approximately 3 dB from said digital audiosignal.
 24. The method of claim 23 wherein said predetermined number ofbits comprise a least significant bit (LSB).
 25. The method of claim 24wherein said predetermined number of bits comprise a most significantbit (MSB).
 26. A computer program product for use in conjunction with acomputer system, the computer program product comprising a computerreadable storage medium and a computer program mechanism embeddedtherein, the computer program mechanism comprising: (a) instructions forobtaining a random number comprising sixteen (16) bits; (b) instructionsfor selecting a predetermined number of bits of said random number; (c)instructions for adding said predetermined number of bits to a firstpulse code modulated audio data of said digital audio signal; and (d)instructions for repeating (a)-(c) until said plurality of pulse codemodulated audio data are processed to produce degraded digital audiosignal, whereby said degraded digital audio signal is degradedapproximately 3 dB from said digital audio signal.
 27. The computerprogram product of claim 26 wherein said random number is generated by arandom number generator comprising linear feedback shift registers(LFSR).
 28. The computer program product of claim 27 wherein saidpredetermined number of bits comprise a least significant bit (LSB). 29.The computer program product of claim 28 wherein said predeterminednumber of bits comprise a most significant bit (MSB).
 30. A system forprogressive quality degradation in reproduction of digital audio signalcomprising a plurality of pulse code modulated audio data, said systemcomprising: a white noise generator to generate white noise; means fordegrading said digital audio signal using said white noise, and wherebysaid white noise is introduced into said digital audio signal so thatrepeated applications of said white noise to said digital audio signalprogressively degrade said digital audio signal.
 31. The system of claim30 wherein said white noise comprises a random number generated by arandom number generator comprising linear feedback shift registers(LFSR).
 32. The system of claim 31 wherein said means for degrading saiddigital audio signal comprises means for adding said random number tosaid digital audio signal.
 33. A system for progressive qualitydegradation in reproduction of digital audio signal comprising aplurality of pulse code modulated audio data, said system comprising: arandom number generator to generate a random number; and a digitalentroping unit for adding said random number to a pulse code modulatedaudio data, whereby entropy of said digital audio signal is increased.34. The system of claim 33 wherein said random number generatorcomprises linear feedback shift registers (LFSR).
 35. The system ofclaim 34 wherein said digital entroping unit further comprising meansfor adding a predetermined number of bits of said random number to saidpulse code modulated audio data.
 36. A method for increasing entropy ofa digital audio signal input to prevent unauthorized reproduction ofsaid digital audio signal comprising generating white noise; and addingsaid white noise to said digital audio signal input to produce a digitalaudio signal output, so that entropy of said digital audio signal outputis increased relative to said digital audio signal input.
 37. The methodof claim 36 wherein said white noise is a random number comprising aplurality of digital bits.
 38. The method of claim 37 wherein apredetermined number of said plurality of digital bits is added to saiddigital audio signal input.
 39. The method of claim 38 wherein saidpredetermined number is an integer or fixed number.
 40. The method ofclaim 39 wherein said adding said predetermined number of said pluralityof digital bits comprises adding a least significant bit of said randomnumber.
 41. The method of claim 40 wherein said adding saidpredetermined number of said plurality of digital bits comprises addinga most significant bit of said random number.
 42. A method forprogressive degradation of a plurality of digital audio data,comprising: generating a number; selecting a predetermined number ofbits of said number; randomly selecting a subset of said plurality ofdigital audio data to which to add said predetermined number of bits;and adding said predetermined number of bits to a digital audio data toproduce a degraded digital audio data.
 43. The method of claim 42wherein said selecting comprises: generating a random number; anddetermining whether to add said predetermined number of bits based uponsaid random number.
 44. The method of claim 43 wherein saidpredetermined number of bits of said number is selected so that saiddegraded digital audio data represents approximately 3 dB differencefrom said digital audio data.
 45. The method of claim 44 wherein saidpredetermined number of bits comprises a least significant bit of saidnumber.
 46. The method of claim 44 wherein said predetermined number ofbits comprises a most significant bit of said number.
 47. A computerprogram product for progressive degradation of a plurality of digitalaudio data, the computer program product comprising a computer readablestorage medium and a computer program mechanism embedded therein, thecomputer program mechanism comprising: instructions for obtaining anumber; instructions for selecting a predetermined number of bits ofsaid number; instructions for randomly selecting a subset of saidplurality of digital audio data to which to add said predeterminednumber of bits; and instructions for adding said predetermined number ofbits to a digital audio data to produce a degraded digital audio data,48. The computer program product of claim 47 wherein said instructionsfor selecting comprises: instructions for generating a random number;and instructions for determining whether to add said predeterminednumber of bits based upon said random number..
 49. The computer programproduct of claim 48 wherein said predetermined number is selected sothat said degraded digital audio data represents approximately 3 dBdifference from said digital audio data.
 50. The computer programproduct of claim 49 wherein said predetermined number of bits comprisesa least significant bit of said number.
 51. The computer program productof claim 50 wherein said predetermined number of bits comprises a mostsignificant bit of said number.